Closed loop method for gold and silver extraction by halogens

a closed loop, gold and silver technology, applied in the direction of electrolysis components, electrolysis processes, process efficiency improvement, etc., can solve the problems of unavoidable sodium accumulation and relatively high capital and operation costs, and achieve the effect of increasing the ph of the barren brin

Active Publication Date: 2015-12-08
DUNDEE SUSTAINABLE TECH
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Problems solved by technology

Therefore at three steps in the above method, namely, at the time of scrubbing the off gases from the chlorination reactor, when precipitating the gold from the pregnant solution and at the time of the purification of the barren solution, the use of sodium hydroxide leads to an unavoidable accumulation of sodium.
Removing sodium sulfate by crystallization is a known process but it is relatively expensive in capital and operation costs.

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  • Closed loop method for gold and silver extraction by halogens
  • Closed loop method for gold and silver extraction by halogens
  • Closed loop method for gold and silver extraction by halogens

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[0020]In a method for gold and silver extraction using halogens, it has been discovered that sodium build-up could be avoided by using a base such as calcium hydroxide Ca(OH)2 rather than sodium hydroxide NaOH i) at the time of scrubbing the off gases from the chlorination reactor, ii) when precipitating the gold / silver from the pregnant solution and iii) at the time of the purification of the barren solution, thereby providing a cost effective closed loop method.

[0021]In a sulfuric acid condition, the resulting neutralization leads to calcium sulfate (gypsum, CaSO4.2H2O), which has a very low solubility in water and can be filtered off easily.

[0022]The use of calcium hydroxide called for the preparation of a slurry of this base which has a tendency to settle, and since the resulting product, gypsum, is not soluble, there was always coating formation of this gypsum around non reacted calcium hydroxides and other particulates in the reaction mixture. This situation called for the use...

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Abstract

A method for extracting precious metals from a polymetallic ore, comprising a) generating hypochlorites from a salt brine; b) chlorination of the ore using hypochlorites under acidic conditions; c) filtering to collect a pregnant solution and treating the pregnant solution for collection of precious metals; d) filtering to separate the precious metals and a barren brine; e) purifying the barren brine; and f) recycling halogens from the purified brine in the form of hypohalites formed by electrolysis of the purified brine, and comprising hypochlorite and hypobromite; step b) further comprising scrubbing excess halogens using calcium hydroxide; treating the pregnant solution in step c) comprises reducing an oxydo reduction potential of the pregnant solution and using calcium hydroxide for neutralization; and step e) comprising increasing the pH of the barren brine by addition of calcium hydroxide.

Description

FIELD OF THE INVENTION[0001]The present invention relates to method for gold and silver extraction by halogens. More specifically, the present invention is concerned with an improved closed loop method for gold and silver extraction by halogens.BACKGROUND OF THE INVENTION[0002]The extraction of gold and silver from polymetallic ores using halogens in brine (NaCl / NaBr in water) has been reported (U.S. Pat. No. 7,537,741).[0003]A closed loop method for extracting precious metals from an ore, using halogens has also been developed, where the halogens (chlorine and bromine) are used as free halogens at the time of extracting the precious metals and are recycled by electrolysis of the barren solution in the form of hypohalides, i.e. sodium hypochlorites NaOCl and sodium hypobromites NaOBr (US Patent application 2013 / 0074655). The free halogens are liberated from the hypohalide state by operating the leaching under acidic conditions. The following equation summarizes the main steps of thi...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C22B3/10C25B1/26C22B11/06C22B3/44C25B1/24
CPCC22B11/06C22B3/44C25B1/24C25B1/26C22B3/22Y02P10/20
Inventor LALANCETTE, JEAN-MARCDUBREUIL, BERTRANDLEMIEUX, DAVID
Owner DUNDEE SUSTAINABLE TECH
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